Eskom’s Mpumalanga Operating Unit will be taking possession of three mobile substations which will be used during fixed type substation refurbishments, maintenance and breakdowns as well as to improve the reliability of the grid network by limiting the duration of power interruptions.

The substations — 40 MVA, 20 MVA and 10 MVA —will be mounted and installed on custom engineered trailers, can be utilised wherever needed within the region to save time, while providing the flexibility of being able to connect to several different high and medium voltage networks.

Built by Zest Energy, managing director, Coenraad Vrey says, “We’re drawing on WEG’s capabilities and experience for this order and [these] broad range of international references gave Eskom peace of mind that we were able to deliver a solution to suit their requirements. In the planning stages of this contract, our design team consulted heavily with Eskom engineers to ensure that we gained a full understanding of their standard specifications and project engineering requirements.”

“The transformer is the specialist aspect of the Eskom units and [we have] been able to come up with a very compact design specific to local conditions.”

The 10 MVA mobile substation en route to Eskom.

Vrey comments that the concept of a purpose-built mobile substation is an ideal solution in this application, because the units can be utilised wherever needed within the region to save time, while providing the flexibility of being able to connect to several different high and medium voltage networks, especially when it comes to interfacing with Eskom’s older networks. This is achieved by using multi-ratio transformers.

The transformers were designed with very low impedances, capable of interfacing with Eskom’s current network infrastructure and limitations. Furthermore, the resulting designs were developed to be robust enough to withstand the internal forces that could be experienced during fault conditions.

The contract includes for the training of Eskom’s drivers on the 20 MVA and the 40 MVA mobile substations, both which have steerable axles for improved manoeuvrability.

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